Grass Yarn

ABSTRACT

The invention relates to grass yarn for artificial grass coverings being a monofilament. These grass yarns can be provided with ridges to reduce light reflection. The grass yarns can also have a sickle shaped cross section for increased strength. The invention further relates to artificial grass covering comprising a plurality of grass yarns according to the invention.

The invention relates to grass yarn for artificial grass coverings orturf coverings. Synthetic grass exists of synthetic blades or fibersthat are attached to a support layer.

The market for artificial turf has seen a rapid development during thelast years due to the numerous advantages of artificial turf abovenatural turf. Growth has been seen in several sport applications,especially in soccer, but also in several kinds of urban applications.

On artificial turf can be played more hours per day, than natural turf.A training pitch provided with artificial turf can be used more intense,such that the number of training pitches can be reduced.

In critical climate situations, like intense heat, very wet or extremecold, artificial grass has proven to be a good solution over naturalgrass.

Where in the beginning of the installation of artificial turf thefunctional properties were mainly important, nowadays the natural lookhas become important as well. Especially in urban and landscapeapplications the optical performance of a grass field has become animportant issue. With regard to the functional properties, the stiffnessof the yarns is one of the important aspects. If the yarns are toflexible, they will fall down. If the yarns are too stiff, they couldhurt the players playing on the artificial turf. Also for a sport field,like a soccer field, the ball—surface interaction is influenced by thestiffness of the yarns. For example how a ball will roll over theartificial turf. Player-surface interactions are also influenced bystiffness, for example a stiff yarn can injure players. In generalstiffness is influenced by the Elasticity-modulus (or Young's modulus)and by the cross sectional inertia. Elasticity modulus is a result oftwo major properties; first the choice of the raw raw materials andsecondly the processing conditions of the yarn.

The first artificial turf coverings were mainly produced with afibrillated tape fiber. These tapes have a rectangular shape, which hasa relative low cross sectional inertia. To arrive at a desired stiffnessof the yarns, the thickness will be such, that the appearance of thetape fibers does not correspond with the appearance of natural grass.

A Second disadvantage of rectangular shapes is the shiny effect. Oftendescribed in the market as plastic look. Several kinds of polymers couldbe used for the production of blades for artificial turf. Polyethyleneis at this moment the most used raw material for artificial grass yarns.Depending on the application also the usage of polypropylene andpolyamide can be seen. Depending on the additives that are used and theproduction method these polymers tend to give the product a shiny look.The plastic look makes the product look cheap. Especially inapplications where no sport properties and only optical properties areimportant the appearance of a grass field is important.

It is an object of the invention to provide a grass yarn for artificialgrass coverings, which has an increased cross sectional inertia and hasa reduced shiny effect.

This object is achieved with a grass yarn being a monofilament.

Monofilament yarns provide an increased design freedom, like in thecross sectional shape, compared to fibrillated tape yarns. Instead ofthe common rectangular cross section of fibrillated tape, monofilamentyarns have the possibility of almost any desired cross section. Acircular cross section or I-shaped cross section has for example ahigher cross sectional inertia and subsequently a higher stiffness, thana rectangular cross section.

It has proven that a monofilament yarn having a cross section in theshape of a semi-circle with a spine in the middle has a good touch and abetter stiffness. However, a disadvantage is that such yarns tend tosplit along the spine after a period of time. Subsequently the stiffnessis no longer maintained and the yarns fall down easily.

According to a preferred embodiment of the invention, the grass yarn (orgrass filament) has a sickle-shaped cross section. With a sickle-shapedcross section, the yarn has a curved cross section with a thick centerpart tapering to both ends. This results in an increased cross sectionalinertia and thus higher stiffness. Also, due to the curved shape, lightis reflected to different directions by the yarn, reducing thereflection.

Another embodiment of the grass yarn according to the inventioncomprises a plurality of ridges arranged on the surface of the grassyarn. These ridges disperse the light such that the reflection of theyarns is reduced.

Preferably the plurality of ridges are arranged in longitudinaldirection of the grass yarn. In combination with monofilament yarns, thelongitudinal ridges can be manufactures easily.

In yet another embodiment of the grass yarn according to the inventionthe height of the ridges is 0.5%-15% of the main thickness of the grassyarn. With the main thickness it is understood the maximum thickness ofthe cross section of the yarn.

The grass yarn according to the invention is preferably of a materialselected from the group high density polyethylene (HDPE), polypropylene(PP), polyamide (PA), polyester and low density polyethylene (LDPE).More preferred, the material of the grass yarn is linear low densitypolyethylene (LLDPE).

In still another preferred embodiment of the invention the linear massdensity of an individual filament is in the range of 50-300 tex.

The invention further relates to an artificial grass covering comprisinga plurality of grass yarns according to the invention.

Preferably, the artificial grass covering according to the inventioncomprises a support layer to which the grass yarns are arranged.

These and other features of the invention, will be elucidated inconjunction with the accompanying drawings.

FIG. 1 shows a cross sectional view of a first embodiment of a grassyarn according to the invention.

FIG. 2 shows a cross sectional view of a second embodiment of a grassyarn according to the invention.

FIG. 3 shows a semi perspective view of an artificial grass coveringaccording to the invention.

FIG. 4A and 4B show further embodiments of grass yarns according to theinvention.

In FIG. 1 a cross sectional view of a first embodiment 1 of a grass yarnis shown. The shape of the grass yarn 1 is sickle-shaped. Thissickle-shaped grass yarn 1 has a thick center portion with a maximumthickness t₁ and two ends tapering into edges 2. The convex side 3 ofthe sickle-shaped grass yarn 1 is provided with ridges 4. The concaveside 5 of the grass yarn 1 is in this embodiment smooth.

The ridges 4 have a thickness t₂. This thickness t₂ is typically0.5%-15% of the thickness t₁ of the sickle shape.

The ridges 4 will scatter light such that the grass yarns according tothe invention will have a light reflection similar to natural grass.Furthermore the curved sickle-shape provides for a high cross sectionalinertia resulting in a relative high stiffness of the grass yarn 1relative to the maximum thickness t₁ of the yarn 1.

In FIG. 2 a second embodiment of a grass yarn 10 according to theinvention is shown. The shape of this grass yarn 10 in cross section isalso sickle shaped. In this embodiment both the convex side 11 as theconcave side 12 are provided with ridges 13 in order to reduce lightreflection.

FIG. 3 shows an embodiment of an artificial grass covering 20. Thisgrass covering 20 has a support layer 21, in which tufts 22, 23 of grassyarns 24. The grass yarns 24 are shown schematically arranged in thesupport layer 21.

In this figure three grass yarns 24 per tuft 22, 23 are shown forexplanation of the invention. Typically 4-12 grass yarns are used pertuft in standard applications of a grass covering according to theinvention.

A typical application of an artificial grass covering according to theinvention has the following characteristics:

Width of a single yarn:1.1 mm

Highest thickness t₁:200 μm

Yarn count individual filament:195 tex 6 of these filaments are twistedor brought together by wrapping. With wrapping a yarn is wound aroundthe 6 filaments.

Raw material used for the yarns is LLDPE (linear Low densityPolyethylene)

The total tex count of a combined yarn after wrapping 6 yarns togetheris 1200 tex.

This combined yarn is used for tufting the following grass carpetconstruction:

Gauge: ⅝′

Stitches: 14 st/10 cm

Pile height:55 mm

Yarn weight:1230 g/m²

It has proven that this product has a very natural look. The yarns donot exhibit any substantial shiny effects. The resulting product istested according the Lisport test as described in standard NF EN 15306;‘Surfaces for outdoor sport areas—Exposure of synthetic turf tosimulated wear’. After 12.200 cycles, no major wear or major yarnsplitting was visible. So it is clear that the sickle-shape of the yarnsaccording to this embodiment reach the object of the invention. Theridges also do not increase the tendency for splitting.

FIG. 4A shows a cross sectional view of third embodiment of a yarn 30according to the invention. This yarn 30 has an ellipse shaped crosssection, being provided with evenly distributed ridges 31 at thesurface.

FIG. 4B shows a cross sectional view of fourth embodiment of a yarn 35according to the invention. This yarn 35 has a rectangular shaped crosssection, being provided with evenly distributed ridges 36 at thesurface.

1. A grass yarn for artificial grass coverings being a monofilament. 2.The grass yarn according to claim 1, wherein the grass yarn has asickle-shaped cross section.
 3. The grass yarn according to claim 1comprising a plurality of ridges arranged on the surface of the grassyarn.
 4. The grass yarn according to claim 3, wherein the plurality ofridges are arranged in a longitudinal direction of the grass yarn. 5.The grass yarn according to claim 3 wherein the height of the ridges0.5%-10% of the main thickness of the grass yarn.
 6. The grass yarnaccording to claim 1, wherein the grass yarn is of a material selectedfrom the group high density polyethylene (HDPE), polypropylene (PP),polyamide (PA), polyester and low density polyethylene (LDPE).
 7. Thegrass yarn according to claim 6, wherein the material is linear lowdensity polyethylene. (LLDPE)
 8. The grass yarn according to claim 1,wherein the linear mass density is in the range of 50-300 tex.
 9. Anartificial grass covering comprising a plurality of grass yarnsaccording to claim
 1. 10. The artificial grass covering according toclaim 9, further comprising a support layer to which the grass yarns arearranged.
 11. The grass yarn according to claim 2, comprising aplurality of ridges arranged on the surface of the grass yarn.
 12. Thegrass yarn according to claim 11, wherein the plurality of ridges arearranged in a longitudinal direction of the grass yarn.
 13. The grassyarn according to claim 11, wherein the height of the ridges is 0.5%-10%of the main thickness of the grass yarn.
 14. The grass yarn according toclaim 4, wherein the height of the ridges is 0.5%-10% of the mainthickness of the grass yarn.